Gaugino searches and SUSY constraints

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Gaugino searches andSUSY constraints
Paolo Azzurri CERN
On behalf of

• Aachen, July 18, 2003
• EPS HEP 2003 - International Europhysics
  Conference
• on high energy
  physics

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R-parity conserved MSSM

• Minimal Supersymmetric extension of the Standard
  Model
• R-parity conserves lepton and baryon numbers.
• ? Stable and weakly interacting LSP (WIMP)
• ? The lightest neutralino is assumed to be the
  LSP
• Candidate for non-baryonic Cold Dark Matter
  (CDM)

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MSSM parameters

• GUT universality of gauginos and sfermions
  reduces the number of fundamental MSSM parameters
  (C-MSSM)

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Impact of LEP1 data
Precision measurements of Z width
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Susy signal searches at LEP2
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Chargino pair searches
4jets, 2jets1lepton, 2leptons Missing
Energy
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Chargino pair candidate
?M26-30 GeV/c2
ECM196 GeV
M(miss)148 GeV/c2
M(hadr)16 GeV/c2
P(µ)8.5 GeV/c
SM WW?t?qq
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Chargino pair results
with heavy sfermions (W decays) combined ADLO
results
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Low ?M chargino searches
The standard searches cover the region
?Mgt3GeV/c2
Searches for soft events with an ISR photon
cover 0.2lt?Mlt3GeV /c2
Searches for events with tracks displaying
kinks, impact parameter offsets, heavy stable
charged particles cover ?Mlt 200MeV /c2
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Neutralino pair searches
Acoplanar jets Acoplanar leptons
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Lower LSP mass limit (with heavy sfermions)
95 CL exclusions from gaugino pair productions
close to the kinematic limit
The lowest not-excluded neutralino-LSP masses are
found in the mixed region at tan?1 and µlt0
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What changes with light sfermions
Chargino pair cross sections decrease and
new decay channels are opened (cascade or
invisible decays as for the
corridor where
is dominant).
_
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Lower LSP mass limit (with light sfermions)
Combined exclusions from LEP1 data (1)
charginos(2) neutralinos(3) sleptons(4) the
(µ,M2,tanß) space is covered in a similar way for
low m0 values as in the case of heavy sfermions
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Impact of Higgs searches
mhltmZ cos2ß radiative corrections from top
and stop
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Impact of mixing on MSSM exclusions (DELPHI)
Previous limits with no-mixing scenario
Stau mixing leads to chargino blind spots when
Search for SUSY signals from
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Impact of stau mixing on MSSM exclusions (ALEPH)
More general approach Stau mixing decoupled from
other families. Study the effects vs mixing angle
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Other lower mass limits
From the same scan of the C-MSSM parameter space
lower mass limits on other SUSY particles can be
obtained
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Robustness of the neutralino-LSP limits

• The unification relation M1/ M2 ?1/2 is driving
  the final result.
• If M1/ M2 lt1/2 the LSP limits deteriorate.
• If M1/ M21 (AMSB) we can find very low
  not-excluded LSP masses
• (E.g. small chargino ?M in gaugino and mixed
  regions)

• Sfermion mass unification is important in the
  case of light sfermions.

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Exclusions in minimal SuperGravity (mSUGRA)

• Dynamic EWSB
• GUT unification of scalar and Higgs sector
• GUT unification of trilinear couplings

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Lower LSP mass limit in mSUGRA
(LEP-208 GeV)
7. Neutralino stau cascades
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Conclusions

• The absence of MSSM signals at LEP2 translate
  into strong constraints on the domains of the
  model parameters and on the gaugino masses

• If sfermions are heavy, direct gaugino searches
  yield a mass limit for the neutralino LSP
  m(?0)gt38-39 GeV/c2 at tan?1 (mixed
  region)
• Same limit with universal light sfermions using
  selectron searches.

• higgs searches exclude low tan? m(?0)gt45
  GeV/c2 (gaugino).

• The exclusions are robust for stau mixing effects

• With full mSUGRA constraints m(?0)gt50-60 GeV/c2
  (gaugino -mixed).